US intelligence services would be allowed to tap text messages, emails and
networking websites under new powers being considered by Barack Obama's
administration.

The FBI says extremists and drug cartels are increasingly communicating online rather than using telephones, leaving US investigators struggling to keep track of them.

A new bill requesting the additional powers to investigate suspected criminals and terrorists will be presented next year. It is likely to face stiff opposition from civil liberties advocates who say the security services have historically abused extensions of power.

James Dempsey, of the pressure group Centre for Democracy and Technology, said: "They are really asking for the authority to redesign services that take advantage of the unique architecture of the internet."

The proposals are likely to require that all encrypted messaging services, such as BlackBerry, include a facility or back door, that would allow investigators to examine communications with a warrant.

Any foreign communications providers operating in America would also have to have an office in the country able to provide intercepts.